Corrosion-resistant nickel-iron alloy

ABSTRACT

ALLOY CONTAINING SPECIALLY PROPORTIONED AMOUNTS OF NICKEL, CHROMIUM, COPPER AND MOLYMDENUM AND OPTIONALLY NIOBIUM ALONG WITH IRON IS CHARACTERIZED BY DESIRABLE COMBINATION OF WORKABILITY, RESISTANCE TO CREVICE CORROSION IN CHLORIDE MEDIA AND RESISTANCE TO CORROSION IN ACIDS.

United States Patent Ofice Patented May 28, 1974 3,813,239 CORROSION-RESISTANT NICKEL-IRON ALLOY George Norman Flint and Thomas Ernest Evans, Solihull,

and Anthony Christopher Hart, Sedgley, England, assignors to The International Nickel Company, Inc.,

New York, N.Y.

No Drawing. Filed Feb. 7, 1973, Ser. No. 330,250 Claims priority, application Great Britain, Feb. 16, 1972, 7,064/72 Int. Cl. C22c 37/00 US. Cl. 75-122 Claims ABSTRACT OF THE DISCLOSURE Alloy containing specially proportioned amounts of nickel, chromium, copper and molybdenum, and optionally niobium, along with iron is characterized by desirable combination of workability, resistance to crevice corrosion in chloride media and resistance to corrosion in acids.

The present invention relates to alloys having good resistance to corrosion in chloride media and in acid media combined with good hot and cold workability and also weldability. There is a demand for such alloys for a wide range of applications in the chemical and other industries. Thus, parts of chemical process plant may be exposed on one side to highly corrosive acid solutions, and on the other to chloride-containing brackish or seawater used for cooling or heating. For this purpose effective resistance is required to stress-corrosion cracking, intergranular corrosion, pitting and crevice corrosion. Resistance to pitting, crevice corrosion and stress-corrosion is also required for articles immersed in seawater, for example, woven wire rope for mooring cables and the like, which additionally require high tensile and yield strength, and cable armouring.

Of these types of corrosion, crevice corrosion is a particularly strong form of attack which can occur in metal or alloy parts possessing recesses or pockets where stagnant liquid can collect. Such recesses may result, for example, where two parts are joined together or where the part meets a gasket or washer, etc. and the liquid which collects may be that in which the part is immersed or a liquid which is being passed through or round the part. Crevice corrosion is particularly likely to occur in chloride containing environments.

An object of the present invention is to provide an economic, corrosion-resistant alloy suitable for these and a wide. range of other uses.

In the present invention it has been found that a highly beneficial combination of workability with resistance to crevice corrosion in chloride media and resistance to corrosion in acids is obtained with alloys having niobium contents less than 1% and copper contents of 1.4% to 3.5% and in which there is a special correlation of the contents of nickel, copper, chromium and molybdenum.

The present invention contemplates a corrosion-resistant alloy containing 33% to 45% nickel and 1.4% to 3.5% copper with the sum of the nickel and copper contents being at least 35%, 14.5% to 20.5 chromium and from 8.5% to 9.5% molybdenum with the value of the relationship:

4[ (percent Cr) +2(percent Mo)] [(percent Ni) (percent Cu) being from 99 to 107, up to 0.9% niobium, up to 0.05% carbon, up to 1% manganese, up to 0.005% boron, up to 0.5% silicon, up to 0.8% titanium, up to 0.7% aluminum, up to 0.05% magnesium, up to 0.8% zirconium, up to 0.05% calcium and balance essentially iron. All percentages herein are by weight.

It is essential that the alloy constituents be carefully correlated in order to achieve the desired combination of properties. Departure from the defined range with respect to any one of the constituents can detrimentally affect one or more of the properties.

. Nickel in an amount of at least 33% is necessary for adequate resistance to crevice corrosion resistance but amounts in excess of 45 unduly increase the cost of the alloys. The nickel content preferably does not exceed 41.5% and more preferably does not exceed 38%.

Copper imparts resistance to corrosion in acid media and an amount of at least 1.4% must be present for this purpose. However an amount in excess of 3.5% impairs the hot workability of the alloys and preferably the copper contents does not exceed 2%. In addition the nickel plus copper content must be at least 35% for adequate resistance to crevice corrosion. The nickel plus copper content preferably does not exceed 43% and more preferably is from 35.4% to 39.4%.

Chromium imparts corrosion resistance in general to the alloys and at least 14.5 is necessary for this purpose, especially with regard to crevice corrosion resistance. Amounts in excess of 20.5% however detrimentally affect crevice corrosion resistance and additionally have an adverse effect on the workability of the alloys. Preferably the chromium content is from 17% to 18%.

Molybdenum must be present in an amount of from 8.5% to 9.5% for imparting resistance to crevice corrosion and amounts below or above this closely defined range are found to adversely affect this property. Amounts in excess of 9.5 molybdenum additionally lead to bad workability. Preferably the molybdenum content does not exceed 9.3%.

In conjunction with the foregoing alloy composition ranges it is also necessary, in order to achieve the desired combination of properties, to correlate the nickel, copper, chromium and molybdenum contents of the alloy so that the value of the relationship:

4[-(percent Cr) +2(percent Mo)] [(percent Ni) (percent Cu)] is from 99 to 107.

Niobium can be optionally present in the alloys in an amount not exceeding 0.9% to stabilize carbides and minimize intergranular corrosion in the welded condition and preferably at least 0.3% niobium is present for this purpose. Carbon can also be present in an amount which, in order to avoid weld decay, must not exceed 0.05%, and preferably should not exceed 0.03%. When the carbon content does not exceed 0.03%, the niobium content is preferably less than 0.7%.

While titanium and aluminum may tend to form oxide inclusions which may impair the surface quality of sheet rolled from the alloys, the presence of one or both of these elements in residual amounts up to 0.8% and up to 0.7% respectively improves the hot-rolling of the alloys and these elements can therefore advantageously be added for this purpose. The residual titanium content is preferably from 0.2% to 0.7% and the residual aluminum content is preferably from 0.05% to 0.15%. Titanium may also act in the alloys as a carbide stabilizer.

Preferred alloys of the invention nominally contain about 35% nickel, 17.5% chromium, 9% molybdenum and 1.7% copper, up to 0.5% niobium, up to 0.5 titanium and up to 0.03% carbon.

The alloys can be made by air melting, desirably in a basic lined high-frequency induction furnace, though vacuum-melting may be used if desired. When air-melting is employed it is beneficial to dcoxidize the alloys with calcium a suitable addition being 0.05% as calcium silicide, nickel-calcium or calcium-aluminum. The retained calcium content should not exceed 0.05% and is advantageously from 0.004% to 0.01%. Silicon can also be employed as a primary deoxidant in its own right. Yet, the residual silicon content of the alloy should not exceed 0.5%

Other elements that may be used for deoxidation in- 4 ferric chloride solution and held therein at a temperature of 60 C. for 40 hours. This test is a searching one and will produce severe corrosion in the crevice areas of materials susceptible to this form of attack. Of six identical samples of the alloy tested, four remained completeclude titanium, aluminum, magnesium, boron, zirconium 5 1y free from attack in the crevice regions, while in the and manganese. Like titanium and aluminum, both magother two cases only a very slight amount of crevice nesium and zirconium tend to form oxide inclusions which corrosion occurred, amounting to less than mg. (millimay impair the surface quality of sheet but magnesium gramme) loss in weight. up to 0.05% or zirconium up to 0.8% can be advantageously used to deoxidize the alloys if they are to be ex- 10 EXAMPLE IV truded before further hot-working. If manganese is used, Foul. alloys (3, 4 A and B) having the compositions no f" than 1% Should be present In the alloys and 1f shown in the Table were vacuum melted, cast as 3 kg. boron 13 used no more than Should ingots 50 mm. in diameter, and extruded in mild steel s examples of alloys accordmg to th mventlon 15 cans at 1200 C. to 16 mm. square bar. The bars were W111 now be glven' heat treated at 1200 C. for /2 hour and quenched in EXAMPLE I water. The remains of the mild steel cans were then A forging ingot 80 mm. (millimeter) in diameter and removed by pickling. Crevice corrosion tests were then weighing 11.5 kg. (kilogramme) was cast from an alloy carried out on specimens of this material. Each specimen containing 33.5% nickel, 17.1% chromium, 8.8% molyb- 20 was of uniform size and consisted of two parts, the first denum, 1.95% copper, 0.48% niobium, 0.035 carbon, of which was a cylindrical sleeve and the second had 0.27% manganese, 0.27% silicon, 0.38% titanium, 0.47% a narrowed piston-shaped portion which was dimenaluminum, 0.005% calcium, with the balance, apart from sioned to fit closely within the first part. The second part impurities, being iron (Alloy No. 1). The alloy was additionally possessed a shoulder on which the first part prepared by vacuum induction melting, including a final could rest, the shoulder being so shaped that a crevice step of deoxidation with calcium. The ingot was forged was formed between the shoulder and the first part. at 1150 C. to 20 mm. thick plate and then hot-rolled to When the two parts were fitted together, the specimen 3 mm. plate. After surface grinding to remove oxidation was essentially cylindrical externally, its diameter being scale, the plate was annealed for one hour at 1150 C., 12.7 mm. and its length being 45 mm. Each specimen descaled in potassium permanganate sodium hydroxide was immersed in 10% ferric chloride solution at 60 solution, and cold-rolled to 1 mm. thick sheet. After C. for 18 hours. Each specimen was weighed before and cold-rolling the sheet material was again annealed for after immersion and the loss in weight is shown in the one hour at 1150 C. Samples cut from the annealed Table.

TABLE Composition (weight percent) Wellght Alloy Ni Cu Cr M0 Nb 0 Mn Si Ti Al Ca (mg? sheet were immersed in boiling aqueous solutions of sul- Comparison of Alloys 3 and 4 those composition is phuric and phosphoric acids for five periods, each of 20 within the invention with Alloys A and B whose composihonrs duration. The average corrosion rates, calculated tion is outside the invention clearly demonstrates the from the loss in weight of the samples, were equivalent superiority of the alloys of the invention in terms of to 0.18 penetration per year in boiling 5% sulphuric acid resistance to crevice corrosion. Comparison of Alloy 3 and 0.25 mm. per year in boiling 75% phosphoric acid. with Alloy B in particular, both of which have similar compositions except for different molybdenum contents, EXAMPLE [II emphasizes the careful control of the molybdenum con- A 3 kg. extrusion ingot cast from the same alloy as in tent necessary to achieve the desired properties. Example I was extruded from 50 mm. diameter to 16 The alloys can be readily hot and cold-worked. Thus mm. diameter, centerless ground to 8.6 mm. diameter and they can be extruded, rolled or forged, for example, cold drawn to wire 0.25 mm. in diameter with anneals at 1150 C., cold-rolled to sheet or strip, cold-drawn to at 1150 C. at various stages during the cold reduction. wire and cold-headed. For optimum cold ductility, hot- The cold reduction obtained in the last pass was in excess worked material should be annealed at about 1150 C., of 95%. The tensile strength of the 0.25 mm. diameter e.g., for about one hour. It is not necessary to waterwire in the as-drawn condition was 1780 MN./m. (megaquench from the annealing temperature, but very slow newton per square meter). cooling such as furnace cooking should be avoided to minimize the risk of structural instability. EXAMPLE III The alloys can readily be welded by the metal-inert A 55 kg. heat of an alloy containing 34.5% nickel, gas and tungsten-inert gas techniques. 17 7% chromium, 5% molybdenum, 1 75% copper, Articles and parts which may advantageously be made 47% i bi 1 carbon, 0,23% manganese, from the alloys include plate heat exchangers, tubular 0.25% silicon, 0.25% titanium, 0.004% calcium, the balheat exchangers. marine wire rope, cable armouring, ance, apart from impurities being iron (Alloy No. 2) was fasteners, evapofators, for Phosphoric acid ch10- prepared by vacuum induction melting, cast to ingots and Tide solutions, P p and P p bleaching P and processed to 1 mm. thick sheet by procedures similar to gical implants The alloys are also useful for forming those described in Example I. Crevice corrosion tests Overlays 0h i which y be subject to Crevice were performed by placing samples 50 mm. x 25 corrosion, e.g., on tube plates, valve seats and variable cut from the annealed sheet material, horizontally be- Pitch p p tween two watch glasses so that the convex surfaces of Although the Present invention has been described in the watch glasses were in contact with the flat surfaces of Conjunction with Preferred embodiments, it is t0 he the sample, thus forming crevices near the points of conunderstood that modifications and variations may be tact. The specimen assemblies were immersed in 1% resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modification and variations are considered to be within the purview and scope of the invention and appended claims.

'We claim:

1. An alloy consisting essentially of 33% to 45% nickel and 1.4% to 3.5% copper with the sum of the nickel and copper contents being at least 35%, 14.5% to 20.5% chromium and from 8.5% to 9.5% molybdenum with the value of the relationship:

4 (percent Cr) 2 (percent Mo) (percent Ni) (percent Cu) being from 99 to 107, up to 0.9% niobium, up to 0.05% carbon, up to 1% manganese, up to 0.005% boron, up to 0.5% silicon, up to 0.8% titanium, up to 0.7% aluminum, up to 0.05% magnesium, up to 0.8% zirconium, up to 0.05 calcium and balance essentially iron.

2. An alloy according to claim 1 wherein the nickel content does not exceed 47.5%, the copper content does not exceed 2% and the sum of the nickel and copper contents does not exceed 43%.

3. An alloy according to claim 2 wherein the nickel content does not exceed 38% 4. An alloy according to claim 2 wherein the sum of the nickel and copper contents is 35.4% to 39.4%.

5. An alloy according to claim 2 containing from 17% to 18% chromium.

6. An alloy according to claim 2 wherein the molybdenum content does not exceed 9.3%

7. An alloy according to claim 2 containing at least 0.3% niobium.

8. An alloy according to claim 1 containing 17% to 18% chromium, not more than 9.3% molybdenum and not more than 38% nickel and wherein the sum of the nickel and copper contents is 35.4% to 39.4%.

9. An alloy according to claim 1 containing nickel, 17.5% chromium, 9% molybdenum and 1.7% copper.

10. An alloy according to claim 9 containing 0.5% niobium, 0.5% titanium and not more than 003% carbon.

References Cited UNITED STATES PATENTS 2,777,766 1/1957 Binder 171 X 3,944,871 7/1962 Mott 75-l25 3,356,542 12/1967 Smith 75171 X L. DEWAYNE RUTLEDGE, Primary Examiner A. I. STEINER, Assistant Examiner U.S. Cl. X.R. 75-134 'F, 171

" UNITED STATES PATENT OFFICE CERTIFICATE OF coRmnwo 3,813,239 May 28, 1974 Patent No. Dated George Norman Flint, v ghomas Ernest Evans and Anthony Christopher Hart It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

r Column 2, line 7, delete second occurrence of "resistance"; and on-same page, line 15, delete letter "s" from the word "contents".

column 3, line 47, for "0.18" read --0.l8 mm-.

Column 5, line 19, claim 2, for "47.5%" read 4lo5% 0 Column 6, line 17, under "References Cited", for

Signed and sealed this 12th day of November 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. 7 C. MARSHALL DANN Attesting Officer Commissioner of Patents 

